US Federal Reserve Chair Janet Yellen has outlined her concerns about the impact of Brexit on the global economy.

Yellen, speaking in Philadelphia on Tuesday at the World Affairs Council, was making her first public comments since last week’s disappointing jobs figure, which undershot market expectations significantly. Experts believe this may have put off a rise in interest rates this month.

She said that one development which “could shift investor sentiment is the upcoming referendum in the United Kingdom. A UK vote to exit the European Union could have significant economic repercussions.”

Looking at the US, Yellen maintained her stance that by and large the labour market had progressed well in the last five years but she says recent developments “bear close watching’.

“Recent signs of a slowdown in job creation bear close watching. Inflation has been lower than our objective of 2 percent, but I expect it to move up over time for reasons that I will describe. If incoming data are consistent with labour market conditions strengthening and inflation making progress toward our 2 percent objective, as I expect, further gradual increases in the federal funds rate are likely to be appropriate and most conducive to meeting and maintaining those objectives.

“However, I will emphasize that monetary policy is not on a preset course and significant shifts in the outlook for the economy would necessitate corresponding shifts in the appropriate path of policy,” she said.

However she listed four challenges to economic prospects with a possible bearing on interest rates.

The thrust and resilience of domestic US demand.

“The U.S. economy has performed better than many others around the globe, and that performance has relied chiefly on the resilience of domestic sources of demand, consumer spending in particular. So an important question is whether the U.S. economy could continue to make progress amid fairly considerable global bumpiness. I continue to think that the answer to that question is yes, but the weak investment performance in recent months is concerning, and Friday’s employment report provides another reminder that the question is still relevant.

The economic situation abroad including the UK

The second uncertainty pertains to the economic situation abroad. Even though the financial stresses that had emanated from abroad at the start of this year have eased, global risks require continued attention. Much of the turmoil early this year appeared to be associated with concern over the outlook for Chinese growth, which in turn has broad implications for commodity prices and global economic growth. Recently, the renminbi has moved in a more predictable fashion and Chinese capital outflows have abated. However, it is widely acknowledged that China faces considerable challenges as it continues to rebalance its economy toward domestic demand and consumption.

“More generally, in the current environment of sluggish growth, low inflation, and already very accommodative monetary policy in many advanced economies, investor perceptions of and appetite for risk can change abruptly. One development that could shift investor sentiment is the upcoming referendum in the United Kingdom. A U.K. vote to exit the European Union could have significant economic repercussions.”

Productivity growth

“A third key uncertainty for the U.S. economy is the outlook for productivity growth–that is, increases in the amount of output produced per hour worked. While the job market has strengthened significantly, GDP increases have been less impressive. That combination of solid labor market gains and moderate GDP growth reflects the fact that labor productivity growth has been unusually weak in recent years, averaging less than 1/2 percent per year since 2010.

“Over time, productivity growth is the key determinant of improvements in living standards, supporting higher pay for workers without increased costs for employers. Recent weak productivity growth likely helps account for the disappointing pace of wage gains during this economic expansion. Therefore, understanding whether, and by how much, productivity growth will pick up is a crucial part of the economic outlook. But this is a very difficult question, and economists are divided. Some are relatively optimistic, pointing to the ongoing pace of innovations that promise revolutionary technologies, from genetically tailored medical therapies to self-driving cars. Others believe that the low-hanging fruit of innovation largely has been picked and that there is simply less scope for further gains.”

“My position has been, and remains, cautiously optimistic. There is some evidence that the deep recession had a long-lasting effect in depressing investment, research and development spending, and the start-up of new firms, and that these factors have, in turn, lowered productivity growth. With time, I expect this effect to ease in a stronger economy. I also see no obvious slowdown in the pace or the potential benefits of innovation in America, which likewise may bear fruit more readily in a stronger economy. In the meantime, it would be helpful to adopt public policies designed to boost productivity. Strengthening education and promoting innovation and investment, public and private, will support longer-term growth in productivity and greater gains in living standards.”

Inflation outlook uncertainty

“A fourth important uncertainty for the economic outlook involves how quickly inflation will move back to 2 percent. As long as oil prices do not resume their earlier declines and the dollar does not rise substantially further, my expectation is that inflation will move up to 2 percent over the next one to two years. But oil prices and the dollar can move unpredictably. In addition, a further strengthening of labor market conditions would typically be estimated to exert modest upward pressure on inflation over the next couple of years; but such estimates are inherently imprecise, and the effect on inflation could turn out to be significantly different, either upward or downward, than I expect.

“Uncertainty concerning the outlook for inflation also reflects, in part, uncertainty about the behavior of those inflation expectations that are relevant to price setting. For two decades, inflation has been relatively stable, reacting less persistently than before to temporary factors like a recession or a swing in oil prices. The most convincing explanation for this stability, in my view, is that longer-term inflation expectations have remained quite stable.12 So it bears noting that some survey measures of longer-term inflation expectations have moved a little lower over the past couple of years, while proxies for these expectations inferred from financial market instruments like inflation-protected securities have moved down more noticeably. It is unclear whether these indicators point to a true decline in those inflation expectations that are relevant for price setting; for example, the financial market measures may reflect changing attitudes toward inflation risk more than actual inflation expectations. But the indicators have moved enough to get my close attention. If inflation expectations really are moving lower, that could call into question whether inflation will move back to 2 percent as quickly as I expect.”

Interest policy implications

Finally assessing the policy implications, she said: “My overall assessment is that the current stance of monetary policy is generally appropriate, in that it is providing support to the economy by encouraging further labor market improvement that will help return inflation to 2 percent. At the same time, I continue to think that the federal funds rate will probably need to rise gradually over time to ensure price stability and maximum sustainable employment in the longer run.”